In recent years, dispersed power sources such as a photovoltaic power generating system have been introduced in, for example, households and office buildings. Such dispersed power sources are interconnected with power systems. Of power generated by the dispersed power sources, power which has not been consumed by loads in the households and office buildings flows back to the power system as surplus power. The surplus power is then sold to a power company. However, if many dispersed power sources are interconnected with a power system, abrupt changes may occur in power flow and voltage due to, for example, reverse power flow from the dispersed power sources and simultaneous parallel off of the dispersed power sources from the power system.
As systems for controlling these changes in power flow and voltage, a microgrid, a virtual power plant, and others are suggested, for example. In these control systems, a power control apparatus for collectively controlling dispersed power sources interconnected with a power system and loads is used (e.g., Patent Literature 1). This power control apparatus performs power flow control for controlling a power flow value at an interconnection point between the dispersed power sources and an upper power system. Moreover, the power control apparatus performs voltage control for controlling a voltage value at a power reception point for the dispersed power source. Specifically, the power control apparatus concurrently calculates a control solution in the power flow control and a control solution in the voltage control, and obtains flow and voltage distribution, using, for example, power flow calculation. If the obtained flow and voltage distribution does not satisfy a constraint, the constraint is changed and the above processing is repeated from the calculation of control solutions. A disturbance in the upper system due to a change in output by the dispersed power sources and a change in load can be reduced by controlling a power flow value based on the calculated control solution in the power flow control. Moreover, power can be stably supplied to each customer in, for example, a virtual power plant, by controlling a voltage value based on the calculated control solution in the voltage control.